NullReferenceException in calls to Barrel.Current.Get for MonkeyCache.FileStore

I’m getting a NullReferenceException on a call to Barrel.Current.Get<T>(key);

I have a very, very async console app that is retrieving a ton of data from our azure devops instance and caching it using MonkeyCache.FileStore. I wound up wrapping it in Polly retries just to get around it.

Stacktrace:

   System.NullReferenceException: Object reference not set to an instance of an object.
           at Interop.BCrypt.BCryptHashData(SafeBCryptHashHandle hHash, ReadOnlySpan`1 pbInput, Int32 cbInput, Int32 dwFlags)
           at System.Security.Cryptography.HashProviderCng.AppendHashData(ReadOnlySpan`1 source)
           at System.Security.Cryptography.HashProvider.AppendHashData(Byte[] data, Int32 offset, Int32 count)
           at System.Security.Cryptography.HashAlgorithm.ComputeHash(Byte[] buffer)
           at MonkeyCache.FileStore.Barrel.Hash(String input)
           at MonkeyCache.FileStore.Barrel.Get[T](String key, Func`2 deserialize)
           at MonkeyCache.FileStore.Barrel.Get[T](String key, JsonSerializerOptions options)
           at GITMigration.Core.Repositories.RepositoryService.<>c__DisplayClass12_0.<GetStatusReponseAndIndexingInformation>b__2() in C:\repos\ResearchAndDevelopment\archtools\gitmigration\GITMigration.Core\Repositories\RepositoryService.cs:line 174
           at Polly.Policy.<>c__DisplayClass114_0`1.<Execute>b__0(Context _, CancellationToken _)
           at Polly.Retry.RetryEngine.Implementation[TResult](Func`3 action, Context context, CancellationToken cancellationToken, ExceptionPredicates shouldRetryExceptionPredicates, ResultPredicates`1 shouldRetryResultPredicates, Action`4 onRetry, Int32 permittedRetryCount, IEnumerable`1 sleepDurationsEnumerable, Func`4 sleepDurationProvider)
           at Polly.Retry.RetryPolicy.Implementation[TResult](Func`3 action, Context context, CancellationToken cancellationToken)
           at Polly.Policy.Execute[TResult](Func`3 action, Context context, CancellationToken cancellationToken)
           at Polly.Policy.Execute[TResult](Func`1 action)
           at GITMigration.Core.Repositories.RepositoryService.GetStatusReponseAndIndexingInformation(String org, String project) in C:\repos\ResearchAndDevelopment\archtools\gitmigration\GITMigration.Core\Repositories\RepositoryService.cs:line 171
           at GITMigration.Core.Repositories.RepositoryService.GetRepoItemsSummary(String org, String project) in C:\repos\ResearchAndDevelopment\archtools\gitmigration\GITMigration.Core\Repositories\RepositoryService.cs:line 35
           at GITMigration.Core.Sheets.Master.MasterWorksheet.GetRow(String org, String project) in C:\repos\ResearchAndDevelopment\archtools\gitmigration\GITMigration.Core\Sheets\Master\MasterWorksheet.cs:line 69
           at GITMigration.Core.Sheets.Master.MasterWorksheet.<>c__DisplayClass7_0.<<AddWorksheet>b__1>d.MoveNext() in C:\repos\ResearchAndDevelopment\archtools\gitmigration\GITMigration.Core\Sheets\Master\MasterWorksheet.cs:line 47
        --- End of stack trace from previous location ---
           at GITMigration.Core.Sheets.Master.MasterWorksheet.AddWorksheet(IExcelBuilder builder, Organization[] orgs) in C:\repos\ResearchAndDevelopment\archtools\gitmigration\GITMigration.Core\Sheets\Master\MasterWorksheet.cs:line 47
           at GitMigration.AsyncConsole.Worker.ExecuteAsync(CancellationToken stoppingToken) in C:\repos\ResearchAndDevelopment\archtools\gitmigration\GitMigration.AsyncConsole\Worker.cs:line 47
           at Microsoft.Extensions.Hosting.Internal.Host.TryExecuteBackgroundServiceAsync(BackgroundService backgroundService)

My “fix” in the calls to the cache:

private async Task<GitPushesResponse> GetLatestGitPushes(string org, string project, string repoId)
{
    string key = $"{org}-{project}-{repoId}-gitpushes";
    var response =
        Policy
            .Handle<NullReferenceException>(ex => ex.Message.Any())
            .Retry((exception, retryCount) => _logger.LogWarning($"Retry Execute GetCache for {key}..."))
            .Execute(() => Barrel.Current.Get<GitPushesResponse>(key));

It’s failing inside of the hashprovider, but succeeds on future calls – so, repeatedly re-running the console app eventually gets me what I need. Happy to look into it if anyone has some ideas.

[vcsjones]

👋 from dotnet/runtime.

Will that still always output the same data?

Yes.

It looks like you’re targeting .NET 6:

https://github.com/jamesmontemagno/monkey-cache/blob/master/src/MonkeyCache.FileStore/MonkeyCache.FileStore.csproj#L4

This API is new in .NET 5. The static HashData is strictly better than using the instances. I’d recommend you use it. The statics are thread safe, they don’t allocate (except the byte[] that gets returned if you use an allocating overload), and they will be faster.

[jamesmontemagno]

So,

I would test what is causing the issue via:

var hashAlgorithm = MD5.Create();

string Hash(string input)
{
	var data = hashAlgorithm.ComputeHash(Encoding.Default.GetBytes(input));
	return BitConverter.ToString(data);
}

Perhaps something is wrong with the input?